This invention relates to the automatic positioning and control of various operating instrumentalities, referred to herein and in the art as "operating heads," that are utilized to move workpieces sequentially through successive cycles wherein various industrial operations perform industrial operations, such as casting, forging, assembly, stamping, welding, and other processes are performed. More particularly, the invention relates to equipment variously referred to as "robots," "manipulators," "pick and place mechanisms," "extractors," "actuators," etc., that are controlled by program tapes and/or by similar automatic control systems, and especially to equipment in which an operating head such as a prehensile "hand," spray head, etc. is carried on an arm capable of several automatically controlled motions to achieve a wide range of travel.
Prior art equipment of the type described often utilizes an operating head, such as tongs or the like, mounted to an arm by a wrist joint that provides tipping motion about an axis perpendicular to the arm and rolling motion about an axis coextensive with the arm. The arm is generally mounted on a pedestal for swinging movement about a vertical axis, for linear extension and retraction relative to the pedestal along the arm axis, and for tilting motion relative to the pedestal about a horizontal axis. The drive for the various motions has usually been provided by various servomechanisms such as hydraulic servocylinders, servomotors, servoactuators, stepping motors, etc.
Usually, the drives for the wrist tipping and rolling motions have been located at the outer end of the arm so that a considerable load must be carried by the arm in addition to the weight of the operating head and the product or load being transported. The stress imposed at the connection between the arm and the pedestal is especially large when the arm is cantilevered out to its maximum extension. This problem requires that the weight of the arm structure be increased to provide the necessary strength.
One approach to the problem of minimizing the load on the arm has been to operate the wrist mechanism through drive tubes extending forwardly to the wrist from a drive system located at the rear of the arm. While this does reduce the weight at the wrist, the weight of the drive tubes still detracts from the load handling capability of the arm. This type of device is disclosed in U.S. Pat. Nos. 3,306,442; 3,306,471; and 3,525,382 to G. C. Devol, Jr.
One limitation inherent in prior art devices is the size of the work zone or envelope within which the operating head can function. Even with a capability of 360 degrees rotation of the arm and a range of extension-retraction of one-half the length of the arm, operation is limited to an annular zone or envelope with a radial depth equal to about one-half the arm length.
A further requirement is the need for sufficient rearward clearance for the arm when the arm is moved to its retracted position.
While the range could be expanded by pivoting a second arm (forearm) at an "elbow" joint on the main arm (upper arm), or by providing a telescoping extension of the main arm, the first system would be complex and add more weight and the second would add considerably to the problem of achieving the wrist movements.
Another problem with prior art devices is that when the operating head is supporting a desired load (workpiece, tool, etc.), and the arm is tilted about a horizontal axis relative to the pedestal, the operating head tilts also, and often places the load in an undesirable attitude. While techniques for compensating for this by performing an automatic reverse tipping of the operating head about the wrist tip axis may be utilized, such compensation using prior art techniques would be complex and extremely costly.
The invention will be shown and described in connection with its application to the die casting industry, and especially to the extraction of newly cast articles from a die casting machine and the subsequent processing of the cast articles. It will be understood that the invention has many other applications, one specific application being reciprocators for use in the die casting industry to carry a fluid emission head through successive operating cycles between the open die platens of a casting machine. The invention would have particular utility in connection with the reciprocator shown in U.S. Pat. No. 4,214,704, owned by the assignee of the present application.
In industrial die casting processes, it is common practice to use a machine to extract castings from a die casting machine. The machines are synchronized with the operation of the die casting machine and are adapted to extend an extractor arm between the opening platens of the casting machine, grasp the casting, retract the arm, and release the casting onto a conveyor belt or into a receptacle or quenching bath. Additional capabilities have been provided for such machines such that, in accordance with recent proposals, programmable industrial robots can be utilized to automatically transport the casting through a complex set of operations.
Another function often performed in die casting operations is the detection of missing parts of castings. Automatic sensing of an incomplete casting immediately after it has been moved from the die is highly advantageous. For this purpose, casting sensors can be located adjacent the die casting machine so that the absence of a section of the casting can be detected.
Performance of the operations described above by machines rather than manually is advantageous from the standpoints of both cost and safety. The safety aspect is particularly significant since the use of machines avoids the necessity for having a worker move between opposed platens of an article forming machine between operating cycles. Typical automatic devices for performing some or all of the functions described above are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 2,998,237 Devol June 13, 1961 3,251,483 Devol May 17, 1967 3,306,442 Devol February 28, 1967 3,306,471 Devol February 28, 1967 3,525,382 Devol August 25, 1970. ______________________________________
Other prior art U.S. patents relating to program-controllable equipment or "robots" are as follows:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,007,097 Shelley et al. October 31, 1961 3,951,271 Mette April 20, 1976 4,214,704 Nagi July 29, 1980. ______________________________________
The apparatus of the present invention resolves many of the difficulties encountered with prior art apparatus, and affords other features and advantages heretofore not obtainable.